The invention relates in general to a method of manufacturing semiconductor devices and, more particularly, to a method of manufacturing a semiconductor device, wherein short problems can be prevented by sufficiently securing a distance between a drain contact plug and a virtual power (VIRPWR) line.
In general, the erase operation of a flash memory device is performed by discharging the electrons of a floating gate from a semiconductor substrate by means of Fowler-Nordheim (F-N) tunneling. The erase operation is performed by applying a high voltage (about 20 V) to the semiconductor substrate. The flash memory device includes a page buffer for reading data stored in a memory cell array. The page buffer is connected to the bit line of the memory cell array through a bit line selection unit.
FIG. 1 is a circuit diagram showing the constriction of a bit line selection unit.
Referring to FIG. 1, an even bit line select transistor HV1 and an odd bit line select transistor HV2 are serially connected between an even bit line BLe and an odd bit line BLo in order to select either of the even bit line BLe and the odd bit line BLo according to even and odd bit line bias signals DISCHe and DISCHo. Virtual power (VIRPWR) is applied to the bit line through the transistors HV1 and HV2. Furthermore, the bit line selection unit includes a connection transistor HV3 for connecting a connection node SO and the even bit line BLe and a connection transistor HV4 for connecting the node SO and the odd bit line BLo. The connection transistor HV3 and the connection transistor HV4 are driven according to the even and odd bit line select signals BSLe and BSLo, respectively. Each of the bit line select transistors HV1 and HV2 and the connection transistors HV3 and HV4 includes a high voltage NMOS transistor. The connection node SO is a connection node of a bit line selection unit and a page buffer.
The bit line selection unit constructed as described above is connected to the junction of the even bit line BLe and the select transistor HV1 at a node Q1. The select transistor HV1 is driven in response to the even bit line bias signal DISCHe, so that a ground voltage Vss or a power supply voltage Vcc applied through the virtual power (VIRPWR) line is applied to the bit line. The bit line selection unit is also connected to the junction of the odd bit line BLo and the select transistor HV2 at a node Q2. The select transistor HV2 is driven in response to the odd bit line bias signal DISCHo, so that the ground voltage Vss or the power supply voltage Vcc supplied through the virtual power (VIRPWR) line is applied to the bit line.
FIG. 2 is a cross-sectional view of a contact plug for connecting the junction of a bit line of a bit line selection unit and a bit line select transistor, and a virtual power (VIRPWR) line.
Referring to FIG. 2, an insulating layer 22 is formed on a semiconductor substrate 21 in which predetermined structures are formed. A contact plug 23, which is connected to the junction (not shown) of a bit line select transistor, is formed at a predetermined region of the insulating layer 22. Furthermore, a bit line 24 and the contact plug 23 are interconnected, and the contact plug 23 and a virtual power (VIRPWR) line 25 are spaced apart from each other at a predetermined distance. In addition, between-the bit line 24 and the virtual power line 25 keeps insulated by means of an insulating layer 26.
In the bit line selection unit having the above-mentioned cross section, however, a distance between the contact plug 23 and the virtual power line 25 that is varied according to the cell operation cannot be secured sufficiently. Accordingly, at the time of a cycling test, a leakage path is formed, resulting in failure in the erase operation. This degrades the reliability of the device.